Hydraulic motor with minimum break-away torque

ABSTRACT

A hydraulic motor device particularly characterized as exhibiting minimum break-away torque under starting or accelerating conditions. The device comprises a housing having an inlet, an outlet at opposite sides. The device also contains a pair of rotary gears in said housing having shaft means disposed on axes of rotation concentric to the bore walls, each rotary gear having alternating gear teeth and gear tooth spaces and being in full meshing engagement with one another. Also present are means to pump fluid under pressure through said inlet and against said teeth whereby said gears are rotated, and at least one arcuate circumferential groove in each bore wall connected to the inlet, and communicating with the teeth of said gears, but having a width less than the width of said teeth. The presence of fluid in the groove reduces startup and running friction at the tips of the gear teeth.

United States Patent 1191 Spencer et a1.

1451 July 17,1973

HYDRAULIC MOTOR WITH MINIMUM BREAK-AWAY TORQUE Inventors: Phillip B.Spencer, Royal Oak; John A. Hovanchak, Detroit, both of Mich.

Assignee: TRW Inc., Cleveland, Ohio Filed: Oct. 14, 1971 Appl. No.:189,399

Related U.S. Application Data Continuation of Ser. No. 887,212, Dec. 22,1969 abandoned.

Trick Aspelin Vickers 418/74 3,285,188 11/1966 Kita 418/74 PrimaryExaminer-Carlton R. Croyle Assistant Examiner-John J. VrablikAttorney-Hill, Sherman, Meroni, Gross & Simpson 57 ABSTRACT A hydraulicmotor device particularly characterized as exhibiting minimum break-awaytorque under starting or accelerating conditions. The device comprises ahousing having an inlet, an outlet at opposite sides. The device alsocontains a pair of rotary gears in said housing having shaft meansdisposed on axes of rotation concentric to the bore walls, each rotarygear having alternating gear teeth and gear tooth spaces and being infull meshing engagement with one another. Also present are means to pumpfluid under pressure through said inlet and against said teeth wherebysaid gears are rotated, and at least one arcuate circumferential groovein each bore wall connected to the inlet, and communicating with theteeth of said gears, but having a width less than the width of saidteeth. The presence of fluid in the groove reduces startup and runningfriction at the tips of the gear teeth.

8 Claims, 6 Drawing Figures PAIENTED JULI 7 i975 sum 1 or 2 HYDRAULICMOTOR WITH MINIMUM BREAK-AWAY TORQUE This a continuation, of applicationSer. No. 887,2l2, filed Dec. 22, 1969 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention is concerned with a hydraulic motor device constructed so asto exhibit minimum break-away torque under starting and acceleratingconditions by reducing startup and running friction.

2. Description of the Prior Art One of the more serious problems foundwith use of a hydraulic motor device is that of excessive breakawaytorque when one initially starts the device or under condition ofacceleration. The primary cause for increase in torque under theseconditions is due to the fact that there is an undesirably high level offriction between the bore walls and the tips of the gear teeth.

A number of proposals have been made to reduce break-away torque inhydraulic motor devices. However, for the most part these have beenunsatisfactory for a number of reasons. In some cases, the constructionof the device is unsatisfactory from the standpoint of complexity, beingtherefore exceptionally costly to manufacture. In other situations,hydraulic motor devices which have been specifically modified to reducebreak-away torque nevertheless still exhibit an undesirably high levelof torque. Thus, the problem has not been completely solved.

It would therefore be a substantial advance in the art if a hydraulicmotor device were devised which obviated the above problem by means of asimple modification of a conventional hydraulic motor device. Moreover,if the device could be simply made such as by casting, it would findready acceptance in the art.

SUMMARY OF THE INVENTION In view of the above, a hydraulic motor devicehas been provided which is particularly characterized as exhibitingminimum break-away torque under starting or accelerating conditions. Thedevice comprises a housing having an inlet, and outlet at oppositesides. The device also contains a pair of rotary gears in said housinghaving shaft means disposed on axes of rotation concentric to the borewalls, each rotary gear having alternating gear teeth and gear toothspaces and being in full meshing engagement with one another. Alsopresent are means to pump fluid under pressure through said inlet andagainst said teeth whereby said gears are rotated, and at least onearcuate circumferential groove in each bore wall connected to the inlet,and communicating with the teeth of said gears, but having a widthlessthan the width of said teeth. The presence of fluid in the groovereduces startup and running friction at the tips of the gear teeth.

It therefore becomes an object of the invention to provide an improvedhydraulic motor device.

A more specific object of the invention is to provide a hydraulic motordevice so constructed that startup and running friction at the tips ofthe gear teeth contacting the bore is considerably reduced leading tominimum break-away torque under starting or accelerating conditions.

"A still further specific object of the invention is to construct ahydraulic motor device which has grooved bore walls, which groovescommunicate with the gear teeth and when filled with fluid reducefriction between the tips of said gear teeth and the bore walls.

Other objects, features and advantages of the invention will be readilyapparent from the following description of certain preferred embodimentsthereof taken in conjunction with the accompanying drawings, althoughvariations and modifications may be effected without departing from thespirit and scope of the novel concepts of this disclosure, and in which:

FIG. 1 is a vertical cross section of the hydraulic motor device of theinvention;

FIG. 2 is a cross section taken across line lI-ll of FIG. 1;

FIG. 3 is another cross section taken across line II-II of FIG. 1illustrating an alternate construction;

FIG. 4 is another vertical cross section of a further embodiment of thehydraulic motor device of the in vention;

FIG. 5 is a cross section taken along lines lV-IV of FIG. 4; and

FIG. 6 is another cross section taken along line IV-IV of FIG. 4illustrating an altemate construction.

Turning now to the drawings, FIG. 1 illustrates one embodiment of theinvention in which there is shown generally the hydraulic motor deviceat 10 which comprises a housing member I2 formed with an inlet 14 and anoutlet 16,- said inlet and outlet being at opposite sides from oneanother in the housing at I8 and 20.

A pair of rotary gears 22 and 24 are rotatably journalled in the housing12 and are carried by shaft members shown respectively at 26 and 28. Theshafts 26 and 28 are disposed on axes of rotation which are concentricwith respect to the bore walls of the lobe 20 and lobe I8 and eachrespective rotary gear is particularly characterized by the formation ofthe peripheral surface thereof of alternating gear teeth 30 and geartooth spaces 32. Thus, the gears 22 and 24 are in full meshingengagement in a nip area of intermesh disposed be tween the inlet 14 andoutlet 16. The inlet 14 communicates with one side of the nip betweenthe gears while the outlet 16 communicates with "the other side of thenip. The inlet and outlet sides of the nip are separated by theintermeshed gear teeth.

In each bore wall 34 and 36, there is shown a groove 37 and 38communicating with the inlet 14 at points 40 and 42. The grooves do notextend the full circumference of the bore but rather terminate at points44 and 46. There is a seal then running from point 44 to 48 and from 46to 50, respectively, defining sealing lands. In the usual case, thesealing lands are approximately 1% tooth spaces from the motor outlet.

The arcuate circumferential constant depth relief notches or grooves arefilled with pressurized fluid and vent the peripheries of the gears toinlet fluid pressure to reduce the startup'and running friction at thetips of the gear teeth, whereby the motor device then exhibits minimumbreak-away torque under starting or acceler ating conditions. Inletpressure thus acts on the gear teeth well beyond the inlet nip area toincrease the gear driving area. By use of such grooves, in effect, thetooth tip contact area is reduced, while driving faces of the gear teethare more exposed to the pressurized fluid. The location of the groovealso forces the gears to one side of the bearings in a direction thatwill not tend to reduce the seal width between the sealing teeth and thehousing, thereby reducing the tendency to seize as pressures areincreased.

The relationship between the grooves and the bores and teeth is bettershown in FIG. 2. Here there is shown grooves 37 and 38, respectively, inbore walls 34 and 36. Also shown is tooth 52 communicating with groove37 and tooth 54 communicating with groove 38. There is also shown astill further embodiment of the invention wherein bearings 56, 58, 60and 62 are provided at each of the first four journal support points tofurther remove friction. These bearings, which are preferablylow-friction needle bearings are between housing 12 and shafts 26 and28.

In FIG. 3 there is shown an alternate device as a section through lineIIII of FIG. 1 wherein each bore has two grooves. The grooves 64 and 66and bore wall 34 communicate with tooth 52. Grooves 68 and 70 and borewall 36 communicate with tooth 54. Again needle bearings 56, 58, 60 and62 are shown between the shafts 26 and housing 12.

In a further embodiment shown in FIG. 4, the hydraulic motor device ofthe invention is so modified to permit dual direction. In addition tothe structures already described there is shown here grooves 72 and 74.Groove 74 is connected to the source of fluid, in this case by port 76and line 78 to pump means 80. Line 78 extends through the housing toconnect with the port 76 which in turn connects with groove 74.Likewise, there is shown groove 72 connecting with line 82 through port84. Again, this groove is supplied with fluid from pump 80 which also isconnected to the inlet means 14. Thus, again groove 72 is supplied withfluid through the inlet means, specifically by means of pump 80. By thepresence of fluid in grooves 72 and 74 the start-up and running frictionat the tips of the gear teeth is greatly reduced.

In this embodiment, the inlet of FIG. 4 is shown at 14 and outlet 16.However, depending on the rotation required, the inlet means and outletmeans can be reversed with ports 76 and 84 being connected to whateverchamber shown in the inlet chamber by means of pump 80. An externalvalve arrangement (not shown) can be utilized to shift the feed lines 78and 82 from pump 80 to the new inlet when direction is changed.

FIGS. and 6 are cross sections of FIG. 4 through line IVIV of FIG. 4.FIG. 5 illustrates the concept of a single groove. FIG. 6 graphicallyshows two arcuate circumferential grooves communicating with each rotarygear.

As shown in FIG. 5, line 82 connects to groove 72 by means of port 84.Also shown in bore wall 34 and tooth 86. Again, on the opposite side,line 78 connects with groove 74 through port 76 where there is alsoshown bore wall 36 and tooth 88. Again, needle bearings 56, 60 and 62are positioned between housing 12 and shafts 26 and 28 at each of thefour points to further reduce friction.

FIG. 6 illustrates an embodiment of the invention utilizing two groovesin the dual directional motor device. These grooves are shown at 90 and92 at the top of the drawing and 94 and 96 at the bottom of the drawing.

It has been determined that the width of the abovediscussed grooveshould have a width less than the width of the gear teeth. If such isnot the case, too much of the tooth surface would be exposed to pressurecausing excessive bearing loads and failure. For optimum safe loadingthe groove width should be of a width less than the width of the teeth,and most preferably is about one-half of the width of the gear teeth. Inthose situations where two grooves are employed are present, the totalwidth of the two grooves again should be less than the width of the gearteeth, and is most satisfactorily about one-half the width of the gearteeth. It is understood, of course, that one may utilize any number ofgrooves other than just one or two grooves as specifically discussedhere.

The device discussed above may be used wherever a low-break-away torquehydraulic motor is required. Low friction at high speeds makes thedevice particularly desirable for use as blowers, fans, gear reductionmechanisms and power rotary devices.

We claim as our invention:

1. A hydraulic motor device exhibiting a minimum break-away torque understarting and accelerating conditions, said device comprising a housinghaving an inlet and outlet at opposite sides, said housing having formedinternally therein a double lobed cavity be tween said outlet and inlet,a pair of rotary gears in said housing having shaft means disposed onaxes of rotation concentric to the bore wall of each lobe, each rotarygear having alternating gear teeth and gear teeth spaces between and infull meshing engagement with one another, means to pump fluid underpressure through said inlet and against said teeth whereby said gearsare rotated, at least one arcuate circumferential groove in each borewall in communication with said means to pump fluid and surrounding theteeth of said gears, said groove extending to a cutoff point spacedbefore the outlet and having a width less than the width of said teethwith the tips of the gear teeth engaging the bore walls of the lobesadjacent the groove along the entire length of the groove whereby thepresence of pressurized fluid in said groove vents the driving sides ofthe gear teeth and the peripheries of the gears to inlet fluid pressureto reduce the startup and running friction at the tips of the gearteeth.

2. A hydraulic motor device according to claim 1, wherein there arepresent a pair of holes in the housing communicating with said groovesin each bore, said feed holes being connected with the inlet means.

3. A hydraulic motor device according to claim I, wherein the grooveextends directly from the inlet to the cutoff point.

4. A hydraulic motor device according to claim 3, wherein the width ofsaid groove in each bore wall is approximately one-half the width of theteeth and surrounds the central portion of the gear teeth.

5. A hydraulic motor device according to claim 1, wherein each bore hasa pair of grooves whose total width is less than the width of the teethwith each groove positioned at an end of a gear.

6. A hydraulic motor device according to claim 5, wherein the totalwidth of said pair of grooves in each bore is approximately one-half thewidth of the teeth.

7. A hydraulic motor device exhibiting a minimum break-away torque understarting and accelerating con ditions, said device comprising a housinghaving an inlet and outlet at opposite sides, said housing formedinternally therein a double lobed cavity between'said inlet and outlet,a pair of rotary gears in said housing having shaft means disposed onaxes of rotation concentric to the bore wall of each lobe, each rotarygear having alternating gear teeth and gear teeth spaces being in fullmeshing engagement with one another, means to pump fluid under pressurethrough said inlet and against said teeth whereby said gears arerotated,

said grooves vents the peripheries of the gears to inlet fluid pressureto reduce the startup and running friction at the tips of the gear teethand to force the gears in a direction that will not reduce the sealwidth of the meshing gear teeth.

8. A hydraulic motor device according to claim 7, wherein the totalwidth of the grooves in each bore wall is approximately one-half thewidth of the teeth.

1. A hydraulic motor device exhibiting a minimum break-away torque understarting and accelerating conditions, said device comprising a housinghaving an inlet and outlet at opposite sides, said housing having formedinternally therein a double lobed cavity between said outlet and inlet,a pair of rotary gears in said housing having shaft means disposed onaxes of rotation concentric to the bore wall of each lobe, each rotarygear having alternating gear teeth and gear teeth spaces between and infull meshing engagement with one another, means to pump fluid underpressure through said inlet and against said teeth whereby said gearsare rotated, at least one arcuate circumferential groove in each borewall in communication with said means to pump fluid and surrounding theteeth of said gears, said groove extending to a cutoff point spacedbefore the outlet and having a width less than the width of said teethwith the tips of the gear teeth engaging the bore walls of the lobesadjacent the groove along the entire length of the groove whereby thepresence of pressurized fluid in said groove vents the driving sides ofthe gear teeth and the peripheries of the gears to inlet fluid pressureto reduce the startup and running friction at the tips of the gearteeth.
 2. A hydraulic motor device according to claim 1, wherein thereare present a pair of holes in the housing communicating with saidgrooves in each bore, said feed holes being connected with the inletmeans.
 3. A hydraulic motor device according to claim 1, wherein thegroove extends directly from the inlet to the cutoff point.
 4. Ahydraulic motor device according to claim 3, wherein the width of saidgroove in each bore wall is approximately one-half the width of theteeth and surrounds the central portion of the gear teeth.
 5. Ahydraulic motor device according to claim 1, wherein each bore has apair of grooves whose total width is less than the width of the teethwith each groove positioned at an end of a gear.
 6. A hydraulic motordevice according to claim 5, wherein the total width of said pair ofgrooves in each bore is approximately one-half the width of the teeth.7. A hydraulic motor device exhibiting a minimum break-away torque understarting and accelerating conditions, said device comprising a housinghaving an inlet and outlet at opposite sides, said housing formedinternally therein a double lobed cavity between said inlet and outlet,a pair of rotary gears in said housing having shaft means disposed onaxes of rotation concentric to the bore wall of each lobe, each rotarygear having alternating gear teeth and gear teeth spaces being in fullmeshing engagement with one another, means to pump fluid under pressurethrough said inlet and against said teeth whereby said gears arerotated, a pair of separated parallel arcuate circumferential grooves ineach bore wall in direct communication with said inlet means andsurrounding the peripheries of the gear teeth at the outer tips of theteeth, said grooves extending from the inlet to a cutoff point spacedbefore the outlet and having a total width less than the width of saidteeth and said gear teeth riding on the cavity walls adjacent thegrooves along the entire length of the grooves whereby the presence ofpressurized fluid in said grooves vents the peripheries of the gears toinlet fluid pressure to reduce the startup and running friction at thetips of the gear teeth and to force the gears in a direction that willnot reduce the seal width of the meshing gear teeth.
 8. A hydraulicmotor device according to claim 7, wherein the total width of thegrooves in each bore walL is approximately one-half the width of theteeth.